WASHINGTON — A crewed mission to the surface of Mars is the only goal that justifies the effort and billions of dollars it will take to send human explorers beyond Earth orbit, a congressionally chartered National Research Council panel concluded in a report published June 4.

During the long slog toward the martian surface, the panel said, NASA should hone its skills by testing the necessary technology at steppingstone destinations such as the Moon and near-Earth asteroids in their native orbits.

The lunar surface, which NASA says is unreachable in the current budget environment, got a shout out in a June 4 press release issued to promote the nearly 300-page report by the NRC’s Committee on Human Spaceflight. The report was titled “Pathways to Exploration — Rationales and Approaches for a U.S. Program of Human Space Exploration.”

“[T]he report found that a return to extended surface operations on the moon would make significant contributions to a strategy ultimately aimed at landing people on Mars, and that it would also likely provide a broad array of opportunities for international and commercial cooperation,” the committee, co-chaired by Cornell University professor Jonathan Lunine and former Indiana Gov. Mitch Daniels, said in the release.

In the NASA Authorization Act of 2010, Congress directed the NRC to produce a high-level review of the U.S. human spaceflight program as a guide for policymakers “over the fiscal year period of 2014 through 2023, while considering the program’s likely evolution in 2015 [through] 2030.” In carrying out that directive, the committee allowed for the possibility that the end goal of a Mars landing might not be realized until halfway through this century.

The White House has insisted since 2010, the year after U.S. President Barack Obama took office, that it is doing exactly what the NRC’s latest report recommends: preparing NASA to land crews on Mars, and developing the technology needed to do it. At the same time, the administration has insisted that it does not need to stop at the lunar surface along the way.

Obama in 2010 canceled the Constellation program that sought to establish a Moon base after a blue-ribbon panel said the approach would require considerably more money than NASA was projected to receive under the budget plans laid out by the previous administration, which had hatched the initiative.

Obama, like his predecessor, George W. Bush, was disinclined to give NASA an annual budget increase in the billions so that the agency could develop a lunar lander.

In 2013, the White House announced plans to send astronauts to the only destination beyond low Earth orbit it deemed affordable: a small asteroid that would be redirected to lunar space by a new robotic spacecraft that would also serve as a technology pathfinder and demonstration vehicle for future Mars logistics craft.

The Asteroid Redirect Mission plan calls for astronauts to visit the captured space rock by 2025, the date by which Obama had previously challenged NASA to send humans to an asteroid. These explorers would be travel inside the Orion deep-space capsule launched by the heavy-lift Space Launch System — vehicles that were mandated by Congress as part of the NASA Authorization Act of 2010.

Even lawmakers who are beginning to warm to the Asteroid Redirect Mission, which met a decidedly chilly reception on Capitol Hill, remain cautious about the concept. Democrats on the House Science Committee are among the friendliest to the program, and they have withheld their official blessing pending a written report from NASA on the program’s costs and risks, and on whether it requires any new technology that could not also be developed as part of a lunar mission. NASA would be required to complete that report 180 days after a bipartisan NASA reauthorization bill now awaiting a vote on the House floor becomes law.

The NRC committee passed no judgment on the Asteroid Redirect Mission. In fact, the mission is one of three assumed starting points from which the report outlines possible paths to the martian surface.

No matter what starting point the agency ultimately settles on, the report says, NASA must mature 10 key capabilities before a crewed Mars landing, and the radiation-soaked interplanetary cruises required both before and after, is feasible. The report placed special emphasis on the first three.

Mars entry, descent, and landing technology, which enables crews and supplies to reach the surface. The most mass NASA has safely set down on Mars is the car-sized Curiosity rover that landed in 2012. A crewed mission would require landing considerably more mass.

Radiation shielding during the cruise and surface-sorties phases of a Mars landing mission.

Next-generation in-space propulsion and power systems.

Heavy-lift launch vehicles.

Planetary ascent propulsion to get crews off the surface of Mars after their mission is over.

A new environmental control and life-support system.

Habitats for crews journeying to and living on Mars.

Extravehicular activity suits, otherwise known as space suits.

Crew health. There are medical unknowns associated with long-duration spaceflight, and Mars surface activities, some of which NASA is investigating aboard the international space station in low-Earth orbit.

In-situ resource utilization, which would entail, for example, using the Mars atmosphere as a source of raw materials for life support systems or propellant.